This invention relates to concrete pumping hopper apparatus and particularly to an automatic wear compensating means for a pivotal valve tube in a pumping concrete hopper.
In the laying of the concrete, various automatic pumping systems have been suggested for movement of the concrete from a transport truck mixer or other original source means to the deposit site. In one particular system, an open top hopper is provided for receiving of concrete from a source such as a truck-mixer. A delivery line, formed of suitable interconnected rigid and flexible piping leads from the hopper to the deposit site. To establish a continuous flow through the line, a pair of pumping piston cylinder units are mounted to the hopper opposite the delivery line and in open communication with the hopper. A swing or shuttle valve means is located within the hopper and alternately connects the delivery line to the two cylinders. The shuttle valve means may include a swinging pipe member pivotally connected to the delivery line and movable between two positions for selectively coupling the opposite end of the shuttle valve pipe to the pair of pumping cylinders. Thus, in operation, the retraction of the piston within the cylinder causes the concrete to be drawn into the cylinder. The shuttle valve pipe is then moved into engagement with such filled or charged cylinder and the piston extended to force the concrete through the valve pipe and into the delivery line. During such latter functioning, the opposite cylinder is filling with concrete, for subsequent discharge into the valve pipe during the charging of the first unit. In such systems, the valve means should maintain a relatively fluid-tight joint at the valve connection to the cylinder to insure the proper concrete mix is delivered from the hopper to the delivery line and the deposit site. Any significant leakage opening the presence of the usual pumping pressures may be such that the liquid within the concrete may be forced from pumped concrete back into the hopper. Such a loss of moisture changes the mix or slump of the concrete as delivered. Under severe leakage conditions, the moisture loss may be sufficient to result in a dry pack within the pumping line, which completely freezes and closes the pumping line. If this occurs, the system, of course, must be shut down and the line cleared. The maintenance and shut down is not only time consuming but relatively costly.
Generally, to minimize such adverse results, the valve means have been formed with hardened metal surfaces having highly machined or finished surfaces. The pumping of a concrete product, however, presents unique problems in connection with maintaining of the sealed condition. Thus, even with machined surfaces and careful construction, wear occurs and may accelerate because of the abrasive character of concrete material.
In one prior art proposal, a wear plate is secured to the hopper with an adjustable mounting of the wear plate to maintain a very rigid support of the wear plate for firm engagement with the swing valve. The construction permits manual adjustment of the wear plate position to compensate for wear. In order to provide the rigidity required, a relatively complex mounting system is required and further requires relatively careful attention during the setting and adjustment of the wear plate. If proper adjustment is not made, precise parallel relationship between the flat wear plate and the tube member is not established, and leakage and wear may, in fact, be accelerated. Further, the fixed wear plates as well as the adjustable wear plates of the prior art present a substantial and significant initial cost, as well as subsequent high maintenance expense and time in a concrete pumping system employing a concrete hopper.
There is, therefore, a very distinct, positive need for an alternative and an improved hopper construction which will eliminate the problems associated with the wear characteristics of existing systems.